Ferris Bueller (Matthew Broderick) is a suave, put-together kid who constantly falls on his feet. Ferris is a senior in a high school in suburban Chicago, Illinois, and towards the end of the school year he decides to fake sickness so that he can stay home from school. His parents believe him when he says he is sick but his sister Jeanie smells a rat because Ferris has pulled this routine so many times before. Ferris persuades his girlfriend Sloane (Mia Sara) and his gloomy, pessimistic best friend Cameron (Alan Ruck) to spend the day in Chicago as a "final fling" before they graduate high school and head of for different colleges. He sets up a complicated system in his bedroom that consists of a stereo system, a trophy and a mannequin just in case anyone should decide to come to the house and check on him. Then he sets about persuading Cameron to let them use his father's beautifully-restored 1961 Ferrari 250 GT to pick Sloane up from school, and he also convinces Cameron to call the school and impersonate Sloane's father, telling them to release Sloane from school immediately because of the death of her grandmother.
The only two people who are not convinced by Ferris' claims of illness are his sister (Jennifer Grey), who is heartily tired of his getting away with defying authority figures, and the school principle, Edward Rooney Jeffrey Jones), who is convinced that Ferris is an habitual truant.
When Ferris, Sloane and Cameron arrive in downtown Chicago they leave the Ferrari with two garage attendants who shortly afterwards take if for a joyride around the city. Ferris and friends take in the city for themselves, going to Wrigley Field to watch a baseball game and taking part in the Von Steuben Day Parade. Ferris also pretends to be the Sausage King of Chicago, Abe Froeman, so that they can dine for free at an upscale restaurant, although this almost backfires when Ferris sees his father dining there as well, with business associates.
Meanwhile, Mr Rooney has become obsessed with the challenge of catching Ferris out in a lie. He leaves the school campus and goes to visit Ferris' home, but he gets stuck in the mud, losing his shoe and wallet and being chased, shoeless and muddy, by the dog. Jeannie comes home as well, looking for Ferris, but instead sees Mr Rooney and doesn't recognize him, believing him to a a burglar and kicking him hard in the face several times before calling the police. Of course, Mr Rooney flees the scene before the police arrive, which means that they assume Jeannie was making a prank call and take her down to the police station. Whilst Jeanie waits for her mother to pick her up she gets talking to a teen delinquent drug dealer (Charlie Sheen), who tells her that she should focus on herself and stop obsessing about her brother. Jeanie is busy making out with him when her mother arrives.
At the end of their big day out in the city, Ferris and the others pick up the Ferrari but see that there are hundreds of additional miles on it. This makes Cameron panic because he is scared his father, who is very abusive, will see the additional mileage and get angry about it. Ferris suggests jacking the car up and running it in reverse, which he believes will reverse the odometer, but his plan does not work at all, and Cameron begins railing and shouting about his father, realizing that is it high time that he stood up to him. He lashes out physically at the front of the car which makes it unbalance and topple into the ravine behind the garage. Ferris offers to go to Cameron's father and take the blame but Cameron will not hear of it and vows to stand up to his father if he needs to.
Ferris takes Sloane home and then sprints across the neighborhood backyards, almost getting hit by a car as he crosses the street. He realizes that his mother and sister are in the car that has nearly hit him, and although his mother hasn't spotted him, his sister has, and she floors the gas pedal trying to beat him home. Ferris arrives home to find Mr Rooney waiting for him, but also finds that his sister has finally come to appreciate his ingenuity. She scolds him in front of Mr Rooney for walking home from the hospital instead of waiting for her to give him a ride. She then thanks Mr Rooney for checking on Ferris and hands him the wallet that he dropped when he was at the house earlier. Mr Rooney is chased by the dog again, giving Ferris the opportunity to race upstairs and take to his bed in time for his parents to come and check on him.
Mr Rooney, disheveled and flustered, is forced to catch a school bus back to school.
